A conventional vehicle heating ventilation and air conditioning unit (Heating Ventilation And Air Conditioning Unit; HVAC unit) is generally configured so as to selectively blow out an air flow whose temperature has been regulated by an evaporator, an air-mix damper, and a heater mounted in an air channel within a unit case into a cabin from a DEF blowing channel, a face blowing channel, and a foot blowing channel that are provided with a DEF damper, a face damper, and a foot damper located downstream of the evaporator, the air-mix damper, and the heater.
Those provided with a side demister that blows out temperature-regulated air towards the side window glass in addition to a defroster that blows out the temperature-regulated air from a DEF blowing channel towards the windshield are configured so that side demister channels that guide the temperature-regulated air to the side window glass are formed at both the right-side portion and the left-side portion of the DEF blowing channel, or so that, as shown in PTL 1, end portions of the side demister ducts are inserted into and retracted from both the right-side portion and the left-side portion of a defroster nozzle body connected to an air conditioning unit, and the shapes of the end portions are orientated so as to face against the flow of the temperature-regulated air within the defroster nozzle body.
With the HVAC unit described above, by opening and closing the DEF damper, the face damper, and the foot damper, the blowing mode of the temperature-regulated air can be selected from any of a DEF mode where the DEF damper is opened, a face mode where the face damper is opened, a foot mode where the foot damper is opened, a DEF/foot mode where both the DEF damper and the foot damper are opened, and a bi-level mode where both the face damper and the foot damper are opened. In the foot mode, which is a heating mode, in order to prevent and clear fogging of the windshield and the side window glass, the DEF damper is set to a small degree of opening, and temperature-regulated air that is about 10 to 20% of the total airflow in the foot mode is supplied towards the DEF blowing channel and the side demister channels.